This invention relates to anaerobically-curing compositions.
Anaerobically-curing compositions generally comprise polymerizable acrylate monomers and free-radical initiators. When maintained in an oxygen-containing environment, such compositions remain uncured (i.e., unpolymerized). However, in the absence of oxygen, such as when an anaerobically-curing composition is placed between surfaces which are in close engagement with one another (e.g. a nut and bolt), cure will ensue.
Anaerobically-curing compositions containing peroxide or hydroperoxide initiators are well-known in the art, having been described in U.S. Pat. No. 2,895,950 (Krieble). Commonly such compositions contain quinone-type compounds which act as polymerization inhibitors, thereby maintaining the compositions in an uncured state when stored in the presence of oxygen.
Unfortunately, anaerobically-curing compositions which contain peroxide or hydroperoxide initiators may possess certain disadvantages. For example, there is often the possibility of explosion whenever large amounts of peroxy compounds are handled such as during manufacture of these compositions. Furthermore, unfortunately peroxy compounds typically decompose with time, thus resulting in a steadily decreasing ability of such compounds to initiate the polymerization of compositions containing them.
While one-part, anaerobically-curing compositions containing polymerization initiators other than peroxy compounds are known in the art, such compositions often fail to exhibit a suitable balance of shelf-life stability versus cure-rate. In particular, while such compositions may exhibit suitable shelf-like stability in the presence of oxygen, they may cure at unsatisfactory rates when oxygen is excluded. Alternatively, such compositions may often cure rapidly in the absence of oxygen, but may exhibit unsatisfactory shelf-lives.